These kinds of hooks are commonly seen on the end of pet leads or for attaching shoulder straps to bags/satchels.
Ideal for use when chain or rope needs to be easily detached and reattached to something.
Used in roofing and maritime applications
Also act as a rust free fixing for use with tiles, natural roof slates or lead
Copper also has a similar life expectance to lead and holds without restricting thermal movement
Manufactured to BS1202